A tunnel lining thickness real-time detection system and method

Abstract

The application discloses a tunnel lining thickness real-time detection system and method, and particularly relates to the field of water conservancy and hydropower engineering tunnel construction quality nondestructive testing technology, and aims to solve the problem that the existing detection method cannot accurately identify the real thickness signal due to not taking into account the water film dielectric mutation effect; the system and method are characterized in that: first frequency and second frequency electromagnetic waves are synchronously emitted to the lining surface, and the intensity difference of the concrete-water film interface reflected waves is obtained; the water film dielectric constant gradient change rate is calculated according to the difference; the electromagnetic wave penetration energy compensation coefficient is determined; the electromagnetic wave emission angle offset value is calculated by combining the tunnel axis inclination and the water film gravity flow direction, and the emission device orientation is adjusted; the received signal is corrected by using the compensation coefficient and the offset value, the effective echo time of the lining-surrounding rock interface is extracted; and finally, the actual thickness of the lining is calculated based on the effective echo time and the reference propagation speed of the electromagnetic wave in the concrete; the water seepage environment interference is effectively overcome, and the real-time high-precision detection of the lining thickness is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of non-destructive testing of tunnel lining thickness in water conservancy and hydropower engineering, and more particularly to a tunnel lining thickness real-time detection system and method. BACKGROUND

[0002] In the construction of water conservancy and hydropower engineering tunnels, the lining concrete structure bears high water pressure loads, and the thickness deviation directly affects the safety of the project, requiring full-process quality control of the lining thickness. The traditional drilling detection method will damage the anti-seepage structure, and when using non-destructive testing technologies such as geological radar or ultrasonic waves, the unique high-pressure seepage environment of water conservancy tunnels causes a continuous water film to exist on the surface of the lining.

[0003] The seepage during the construction of water conservancy tunnels forms a stable water film on the surface of the lining, causing abnormal strong reflection of electromagnetic waves / ultrasonic waves at the concrete-water film interface. The current detection method does not take into account the dielectric sudden change effect of the water film, resulting in attenuation of the effective echo energy of the lining-surrounding rock interface in the received signal, and the true thickness signal cannot be accurately identified. SUMMARY

[0004] In order to overcome the above-mentioned defects of the prior art, the present application provides a tunnel lining thickness real-time detection system and method to solve the problems raised in the background art.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] A tunnel lining thickness real-time detection method, comprising the following steps:

[0007] S1, synchronously emitting first frequency electromagnetic waves and second frequency electromagnetic waves to the lining surface, and obtaining the double-frequency reflection wave intensity difference of the concrete-water film interface;

[0008] S2, calculating the water film dielectric constant gradient change rate according to the double-frequency reflection wave intensity difference;

[0009] S3, determining the electromagnetic wave penetration energy compensation coefficient based on the water film dielectric constant gradient change rate;

[0010] S4, calculating the electromagnetic wave emission angle offset value according to the tunnel axis inclination angle and the water film gravity flow direction, and adjusting the orientation of the electromagnetic wave emission device;

[0011] S5, correcting the original electromagnetic wave signal collected by the receiving end using the electromagnetic wave penetration energy compensation coefficient and the electromagnetic wave emission angle offset value, and extracting the effective echo time of the lining-surrounding rock interface;

[0012] S6, calculating the actual thickness of the lining according to the effective echo time and the reference propagation speed of the electromagnetic wave in the concrete.

[0013] Further, the first frequency electromagnetic wave and the second frequency electromagnetic wave are synchronously emitted to the lining surface to obtain a dual-frequency reflected wave intensity difference of the concrete-water film interface, including:

[0014] The first frequency electromagnetic wave and the second frequency electromagnetic wave are synchronously emitted in a direction perpendicular to the lining surface;

[0015] The first frequency reflected wave intensity value and the second frequency reflected wave intensity value are collected at the same receiving point of the concrete-water film interface by the receiving end;

[0016] The algebraic difference between the first frequency reflected wave intensity value and the second frequency reflected wave intensity value is taken as the dual-frequency reflected wave intensity difference.

[0017] Further, the frequency range of the first frequency electromagnetic wave is 100MHz to 200MHz, and the frequency range of the second frequency electromagnetic wave is 500MHz to 600MHz.

[0018] Further, the water film dielectric constant gradient change rate is calculated according to the dual-frequency reflected wave intensity difference, including:

[0019] Based on a fixed difference between the concrete dielectric constant reference value and the relative dielectric constant of water, a linear mapping relationship between the dual-frequency reflected wave intensity difference and the dielectric constant change is established;

[0020] The dual-frequency reflected wave intensity difference is input into the linear mapping relationship, and the water film dielectric constant change amount is output;

[0021] The water film dielectric constant change amount is divided by the frequency difference between the first frequency electromagnetic wave and the second frequency electromagnetic wave to obtain the water film dielectric constant gradient change rate.

[0022] Further, the electromagnetic wave penetration energy compensation coefficient is determined based on the water film dielectric constant gradient change rate, including:

[0023] A positive proportional relationship between the water film dielectric constant gradient change rate and the electromagnetic wave energy attenuation rate is established;

[0024] The water film dielectric constant gradient change rate is multiplied by a proportional constant to obtain a basic compensation coefficient;

[0025] A fixed constant is superimposed on the basic compensation coefficient to form the electromagnetic wave penetration energy compensation coefficient.

[0026] Further, the proportional constant is calibrated through a comparative test of dry concrete test blocks and water-containing concrete test blocks.

[0027] Further, the electromagnetic wave emission angle offset value is calculated according to the tunnel axis inclination angle and the water film gravity flow direction, and the electromagnetic wave emission device is adjusted in orientation, including:

[0028] Read the tunnel axis inclination in the design drawing, and fix the water film gravity flow direction as the vertical downward direction;

[0029] Based on Newton's law of motion, the vector composition relationship between the tunnel axis inclination and the water film gravity flow direction is established;

[0030] The angle between the normal direction perpendicular to the lining surface and the reverse direction of the combined vector direction of the water film gravity flow is calculated as the electromagnetic wave emission angle offset value;

[0031] The electromagnetic wave emission device is driven to adjust the direction to the normal direction superimposed with the electromagnetic wave emission angle offset value.

[0032] Further, the original electromagnetic wave signal collected by the receiving end is corrected by using the electromagnetic wave penetration energy compensation coefficient and the electromagnetic wave emission angle offset value, and the effective echo time of the lining-surrounding rock interface is extracted, including:

[0033] The amplitude of the original electromagnetic wave signal is multiplied by the electromagnetic wave penetration energy compensation coefficient to compensate the energy;

[0034] Based on the electromagnetic wave emission angle offset value, the center frequency of the band-pass filter is set, and the energy-compensated signal is spatially directionally filtered;

[0035] The lining-surrounding rock interface reflection peak point is detected in the time domain waveform of the filtered signal, and the time corresponding to the lining-surrounding rock interface reflection peak point is recorded as the effective echo time;

[0036] The correspondence between the center frequency of the band-pass filter and the electromagnetic wave emission angle offset value is calibrated through antenna directional diagram test.

[0037] Further, the actual thickness of the lining is calculated according to the effective echo time and the reference propagation speed of the electromagnetic wave in the concrete, including:

[0038] The effective echo time of the lining-surrounding rock interface is obtained, and the pre-stored reference propagation speed of the electromagnetic wave in the concrete is called;

[0039] The effective echo time is multiplied by the reference propagation speed to obtain the original thickness value;

[0040] The time domain waveform starting point offset of the original thickness value is calibrated based on the fixed distance from the transmitting end to the lining surface;

[0041] The calibrated original thickness value is taken as the actual thickness of the lining.

[0042] On the other hand, the present application provides a tunnel lining thickness real-time detection system, comprising the following modules:

[0043] The double-frequency reflection module is used for synchronously emitting electromagnetic waves of a first frequency and electromagnetic waves of a second frequency to a lining surface, and obtaining a double-frequency reflection wave intensity difference of a concrete-water film interface;

[0044] The dielectric gradient module is used for calculating a water film dielectric constant gradient change rate according to the double-frequency reflection wave intensity difference;

[0045] The compensation calculation module is used for determining an electromagnetic wave penetration energy compensation coefficient based on the water film dielectric constant gradient change rate;

[0046] The angle biasing module is used for calculating an electromagnetic wave emission angle biasing value according to a tunnel axis inclination angle and a water film gravity flow direction, and adjusting an electromagnetic wave emission device orientation;

[0047] The echo extraction module is used for correcting original electromagnetic wave signals collected at a receiving end by using the electromagnetic wave penetration energy compensation coefficient and the electromagnetic wave emission angle biasing value, and extracting an effective echo time of a lining-surrounding rock interface;

[0048] The thickness calculation module is used for calculating an actual lining thickness according to the effective echo time and a benchmark propagation speed of electromagnetic waves in concrete.

[0049] Compared with the prior art, the present application has the following beneficial effects:

[0050] 1. By synchronously emitting double-frequency electromagnetic waves and capturing reflection wave intensity differences of a concrete-water film interface, the dielectric mutation effect of the water film can be directly quantified. The echo energy recognition capability of a lining-surrounding rock interface is significantly enhanced. The double-frequency difference value accurately captures the water film dielectric constant gradient change rate, which is converted into an electromagnetic wave penetration energy compensation coefficient, effectively offsets the abnormal reflection attenuation problem caused by the water film, and ensures that the received signals are not distorted in a high-pressure water seepage environment. The energy compensation mechanism of the electromagnetic waves compensates for the defects of ignoring the dielectric change of the water film in traditional nondestructive testing, greatly improves the extraction accuracy of the lining thickness signals, makes the entire detection process immune to water seepage interference, and guarantees the reliability of the concrete structure under high water pressure load.

[0051] 2. The electromagnetic wave emission angle is adaptively adjusted in combination with dynamic parameters of the tunnel axis inclination angle and the water film gravity flow direction, the beam directivity is optimized, and signal distortion caused by the water film interface is avoided. This biasing correction and energy compensation realize accurate reconstruction of the original signals at the receiving end, reliably extract the effective echo time of the lining-surrounding rock interface, and use the benchmark propagation speed to inverse the actual thickness. This process constructs a full-automatic closed-loop system, maintains the high robustness of the detection results in a water seepage flow environment, and completes real-time nondestructive monitoring of the lining thickness. It supports quality control during the entire construction period, eliminates engineering hidden dangers caused by thickness deviation, and improves the long-term safety of the water conservancy tunnel anti-seepage structure. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1A flow chart of a tunnel lining thickness real-time detection method of the present application;

[0053] Figure 2 A structural schematic diagram of a tunnel lining thickness real-time detection system of the present application. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present application.

[0055] Embodiment 1: Figure 1 A tunnel lining thickness real-time detection method of the present application is given, which comprises the following steps:

[0056] S1, synchronously emitting first frequency electromagnetic waves and second frequency electromagnetic waves to the lining surface, and obtaining a double-frequency reflected wave intensity difference of the concrete-water film interface;

[0057] S2, calculating a water film dielectric constant gradient change rate according to the double-frequency reflected wave intensity difference;

[0058] S3, determining an electromagnetic wave penetration energy compensation coefficient based on the water film dielectric constant gradient change rate;

[0059] S4, calculating an electromagnetic wave emission angle offset value according to a tunnel axis inclination angle and a water film gravity flow direction, and adjusting an electromagnetic wave emission device orientation;

[0060] S5, correcting original electromagnetic wave signals collected by a receiving end by using the electromagnetic wave penetration energy compensation coefficient and the electromagnetic wave emission angle offset value, and extracting an effective echo time of the lining-surrounding rock interface;

[0061] S6, calculating an actual lining thickness according to the effective echo time and a reference propagation speed of the electromagnetic wave in the concrete.

[0062] The two-channel signal generator is used to generate continuous wave signals of the two frequencies when synchronously transmitting the first frequency electromagnetic wave and the second frequency electromagnetic wave to the lining surface. The frequency of the first frequency electromagnetic wave is selected in the range of 100-200 MHz, for example, 150 MHz, and the selection is based on the fact that the skin depth of the electromagnetic wave in the water-containing concrete meets the detection requirements of the water film. The frequency of the second frequency electromagnetic wave is selected in the range of 500-600 MHz, for example, 550 MHz, and the selection is based on the fact that the signal-to-noise ratio of the reflection signal of the concrete-water film interface at this frequency is higher than that at other frequencies. The two output ports of the two-channel signal generator are respectively connected to the two feed points of the wideband transmitting antenna, and the phase delay of the two signals is controlled by the internal clock synchronization module to ensure that the transmission start time of the first frequency electromagnetic wave and the second frequency electromagnetic wave is synchronized with a deviation of less than 1 ns. The radiation direction of the transmitting antenna is adjusted to be perpendicular to the lining surface by an adjustable support, and the specific operation includes: installing an electronic level at the bottom of the support, and locking the position of the support when the inclination angle displayed by the electronic level is less than 0.5 degrees; and simultaneously measuring the distance between the antenna radiation surface and the lining surface by a laser range finder, and controlling the distance to be in the range of, for example, 50-100 mm.

[0063] After the electromagnetic wave transmission is completed, the reflection signal is collected at the concrete-water film interface by the receiving end. The receiving end uses a double-port receiving antenna, and the horizontal offset distance between the center point of the antenna and the center point of the transmitting antenna is fixed at, for example, 50 mm by a mechanical positioning slot. The first output end of the receiving antenna is connected to a first detector, and the working frequency band of the first detector is 90-210 MHz, which is used to extract the first frequency reflection wave signal; the second output end of the receiving antenna is connected to a second detector, and the working frequency band of the second detector is 490-610 MHz, which is used to extract the second frequency reflection wave signal. The output ends of the two detectors are connected to the differential input channels of a data acquisition system, and the data acquisition system synchronously records the voltage instantaneous values of the two channels at a sampling rate of 1 GHz / s. When the electromagnetic wave forms a reflection wave peak at the concrete-water film interface, the data acquisition system performs the following operations: identifying the reflection wave peak position in the time domain waveform, and taking, for example, a 20 ns time window centered on the position; calculating the root mean square of the voltage instantaneous value of the first channel in the time window as the first frequency reflection wave intensity value; and calculating the root mean square of the voltage instantaneous value of the second channel as the second frequency reflection wave intensity value. The units of the first frequency reflection wave intensity value and the second frequency reflection wave intensity value are both volts.

[0064] The obtained first frequency reflected wave intensity value and the second frequency reflected wave intensity value are input into a subtraction operation unit. The subtraction operation unit is built by an operational amplifier, the non-inverting input terminal of which is connected to the voltage signal corresponding to the first frequency reflected wave intensity value, and the inverting input terminal of which is connected to the voltage signal corresponding to the second frequency reflected wave intensity value. The ratio of the feedback resistance to the input resistance is set to 1:1 to achieve unit gain. The output voltage value of the operational amplifier is the algebraic difference between the first frequency reflected wave intensity value and the second frequency reflected wave intensity value, which is quantized into a digital signal by an analog-to-digital converter and stored as a dual-frequency reflected wave intensity difference value. The dual-frequency reflected wave intensity difference value has a dimension of volts, and its numerical range is adjusted by a preprogrammable gain amplifier, for example, the gain is set to 0.5 to 2 times, so that the output voltage peak value is limited within the full-scale range of the analog-to-digital converter.

[0065] The synchronization performance of the dual-channel signal generator is verified by connecting the two RF output terminals of the signal generator to the two input channels of a spectrum analyzer, setting the spectrum analyzer to time domain scanning mode, and triggering the first channel signal rising edge. When the signal generator outputs, for example, 150 MHz and 550 MHz continuous waves, the spectrum analyzer measures the time interval from the trigger point to the first peak of the two signals, for example, the measured time deviation is 0.8 ns. The perpendicularity of the transmitting antenna to the lining surface is calibrated by a three-dimensional coordinate measuring instrument: paste a reflective marker point on the lining surface, after the coordinate measuring instrument establishes a space coordinate system, measure the included angle between the normal vector of the transmitting antenna radiation surface and the normal of the lining surface at the marker point, for example, the measured included angle is 1.2 degrees.

[0066] When a linear mapping relationship is established based on the fixed difference between the concrete dielectric constant reference value and the relative dielectric constant of water, the pre-stored concrete dielectric constant reference value is first called. This reference value is obtained by measuring a dry concrete standard test block in a laboratory environment, and the specific method is as follows: a vector network analyzer is used to transmit a 1 GHz broadband sweep signal to the standard test block, and the dielectric constant real part is calculated according to the phase shift of the reflection coefficient, for example, a typical value of 8.5 is obtained. The relative dielectric constant of water is taken as a physical constant of 80, and the fixed difference between the two is 71.5 (calculation formula: 80-8.5=71.5). The establishment process of the linear mapping relationship is as follows: prepare concrete test blocks with different water contents (water content range, for example, 5% to 25%), measure the dual-frequency reflected wave intensity difference of each test block at 150 MHz and 550 MHz; simultaneously measure the dielectric constant change of the water film on the surface of the test block directly by the capacitance probe method; input multiple sets of measurement data into the least squares fitting program to obtain the linear relationship: dielectric constant change = slope parameter × dual-frequency reflected wave intensity difference + intercept parameter. The slope parameter is calculated by fitting, for example, a typical value of 0.15 per volt; the intercept parameter approaches zero (less than 0.01) and can be ignored, and the final linear mapping relationship is dielectric constant change = 0.15 × dual-frequency reflected wave intensity difference.

[0067] When the difference between the intensities of the two-frequency reflected waves is input into the linear mapping relationship, signal scaling is realized through a programmable gain amplifier. Specifically, the difference between the intensities of the two-frequency reflected waves is input into the in-phase terminal of the amplifier in the form of a voltage signal, and the gain resistor network of the amplifier is set to a fixed ratio, for example, when the slope parameter is 0.15, the gain value is configured to be 0.15 times (corresponding to a resistance ratio Rf / Ri=0.15). The output voltage value of the amplifier is the change in the dielectric constant of the water film, which is a dimensionless value, and the value range is controlled by the pre-attenuation circuit to be, for example, between 0 and 12, corresponding to a dielectric constant change of 0 to 1.8 (calculation formula: 0.15x12=1.8). The output voltage is quantized into a digital signal by a 12-bit analog-to-digital converter, and the conversion reference voltage is set to 5 volts, with a quantization resolution of 1.22 millivolts.

[0068] When calculating the gradient change rate of the dielectric constant of the water film, first, the frequency difference between the first frequency electromagnetic wave and the second frequency electromagnetic wave is obtained. The difference is fixed at 400 megahertz (calculation formula: 550 megahertz-150 megahertz=400 megahertz), and is stored in a non-volatile memory. The operation of dividing the change in the dielectric constant by the frequency difference is realized by a digital signal processor: the dielectric constant change value output by the analog-to-digital converter is stored in register A; the frequency difference 400 megahertz is converted to the value 4x10 8 , which is stored in register B; the processor executes the division instruction, divides the value in register A by the value in register B, and the calculation result is stored in register C. The value in register C is the gradient change rate of the dielectric constant of the water film, which has a dimension of change per megahertz unit, for example, when the dielectric constant change is 1.2, the gradient change rate is 3x10 -9 8 =3x10 -9 ). The calculation result is output after range checking, and the checking condition is that the absolute value of the gradient change rate is less than 10 -7 , and if it exceeds the limit, the data exception flag is triggered.

[0069] The preparation of the dry concrete standard test block conforms to the ASTM C192 standard: cement, sand, and stone are mixed in a ratio of 1:2:3, the water-cement ratio is 0.45, and after curing for 28 days, it is placed in a 105 degree Celsius oven for drying for 48 hours. The dielectric constant is measured using the coaxial probe method: the probe is tightly pressed against the surface of the test block, and the network analyzer (such as Keysight N5221A) is scanned in the frequency range of 100 megahertz to 1 gigahertz, and the dielectric constant real part is calculated according to the input reflection coefficient:

[0070] ;

[0071] where, represents the reflection coefficient phase angle, ​denotes the real part of the dielectric constant, denotes the input reflection coefficient.

[0072] At 150 MHz, the measurement is repeated 5 times, for example, the data sequence [8.47, 8.52, 8.49, 8.53, 8.50] is obtained, and the arithmetic mean 8.50 is taken as the reference value.

[0073] When the proportional relationship between the dielectric constant gradient change rate of the water film and the energy attenuation rate of the electromagnetic wave is established, based on the attenuation mechanism of electromagnetic wave propagation in the medium: when the electromagnetic wave passes through the water film layer with gradient change of dielectric constant, the energy attenuation rate is linearly and positively correlated with the dielectric constant gradient change rate of the water film. The physical basis of this relationship is derived from the differential form of Maxwell's equations, and the specific implementation is: a proportional constant is pre-stored in the data processing unit, which is calibrated through the comparative test of dry concrete test blocks and water-containing concrete test blocks. The operation process of the calibration test includes: preparing three groups of standard concrete test blocks, the first group is completely dry test blocks (water content 0%), the second group is uniform water-containing test blocks (water content 10%), and the third group is gradient water-containing test blocks (water content 20% on the surface and decreasing to 5% inside); respectively measuring the electromagnetic wave penetration energy attenuation values of each group of test blocks; synchronously measuring the dielectric constant gradient change rate of the water film of the third group of test blocks; fitting multiple sets of data into a linear equation: energy attenuation rate = proportional constant × dielectric constant gradient change rate of water film + background attenuation value. The background attenuation value is taken as the measurement result of the dry test block, and the proportional constant is calculated by the slope.

[0074] The operation of multiplying the dielectric constant gradient change rate of the water film by the proportional constant to obtain the basic compensation coefficient is realized by an analog multiplication circuit. The specific process is: the dielectric constant gradient change rate of the water film is input into the X port of the multiplier in the form of a voltage signal, the proportional constant is input into the Y port in the form of a fixed reference voltage, and the product voltage signal is generated at the output end of the multiplier. The voltage value of the proportional constant is set by a digital potentiometer, for example, when the calibration test obtains a proportional constant of 0.02, the digital potentiometer is configured to generate a 2.0-volt reference voltage (corresponding to a proportional constant of 0.02 volts per unit gradient change rate). The multiplier chip AD633 is selected, and its output calculation formula is: product voltage = (X input voltage × Y input voltage) / 10 volts. When the input voltage corresponding to the dielectric constant gradient change rate of the water film is, for example, 1.5 volts (representing a gradient change rate of 3 × 10 -9 ), and the proportional constant corresponds to a voltage of 2.0 volts, the output basic compensation coefficient voltage value is calculated as (1.5 × 2.0) / 10 = 0.3 volts. The voltage value is buffered by a voltage follower and input into the addition circuit.

[0075] When the electromagnetic wave penetration energy compensation coefficient is formed by superimposing a fixed constant on the basic compensation coefficient, an operational amplifier is used to build an addition circuit. The fixed constant is 1.0, and a 1.000-volt direct current voltage is generated by a precision reference voltage source. The addition circuit is configured as follows: the basic compensation coefficient voltage signal is connected to the inverting input terminal, the fixed constant voltage is connected to the non-inverting input terminal, and the feedback resistance and the input resistance are set to a ratio of 1:1. According to the characteristics of the operational amplifier addition circuit, the output voltage = fixed constant voltage - basic compensation coefficient voltage. When the basic compensation coefficient voltage is 0.3 volts, the output voltage is 1.000-0.3 = 0.7 volts, which is the electromagnetic wave penetration energy compensation coefficient. The compensation coefficient is a dimensionless multiple, and its value range is limited to the interval of 0.5 to 1.5, and overvoltage protection is realized through the clamping diode circuit at the output end.

[0076] Details of the calibration test of the proportionality constant

[0077] Dry test block: standard concrete test block dried in an oven at 105 degrees Celsius for 48 hours, and sealed after cooling;

[0078] Uniform water content test block: immerse the dry test block in deionized water for 24 hours, and wipe off the surface water;

[0079] Gradient water content test block: use the spray soaking method to control the surface water content, for example, spray 0.5 milliliters of deionized water on the surface of the test block, and let it penetrate for 2 hours to form a gradient distribution.

[0080] The energy attenuation rate measurement method uses the penetration method: the transmitting antenna is placed close to one side of the test block, and the receiving antenna is placed on the other side. The measurement steps are as follows:

[0081] Transmit 150 megahertz continuous wave, record the receiving end voltage amplitude ;

[0082] Remove the test block and measure the air path receiving voltage at the same position ;

[0083] The energy attenuation rate is calculated as:

[0084] ;

[0085] Where, is the energy attenuation rate; for example, the dry test block measured an attenuation rate of -2.5 decibels, and the gradient water content test block measured -5.8 decibels.

[0086] When reading the tunnel axis inclination in the design drawing, the engineering drawing analysis software is used to import the tunnel structure design file. The design file is in the computer-aided design format, such as the file format with the extension name of dwg. The analysis software extracts the angle value in the annotation text by identifying the axis annotation layer in the drawing. The angle value represents the angle between the tunnel axis and the horizontal plane, and the measurement unit is degree, and the value range is, for example, negative 30 degrees to positive 30 degrees, and the negative value represents the downhill direction, and the positive value represents the uphill direction. The extracted tunnel axis inclination is stored in the random access memory, waiting for the vector calculation call. The water film gravity flow direction is fixed as the vertical downward direction, which is defined as the vector direction in the three-dimensional coordinate system, such as the vector in the right-handed Cartesian coordinate system, and the components of the vector are 0, -1, and 0, respectively.

[0087] When establishing the vector composition relationship between the tunnel axis inclination and the water film gravity flow direction based on Newton's law of motion, a local coordinate system of the lining surface is first established. The lining surface detection point is taken as the coordinate origin, the tunnel axis direction is taken as the axis direction, and the vertical upward direction is taken as the axis direction, and the axis direction is determined according to the right-hand rule. In the local coordinate system, the water film gravity flow direction vector is represented as. The tunnel axis inclination is converted into the direction vector: when the inclination is, the axis direction vector is. According to Newton's first law, the actual flow direction of the water film under the action of gravity and the support force of the lining surface is the projection direction of the gravity vector on the tangent plane of the lining surface. The projection calculation is realized by vector decomposition: first, the dot product of the gravity vector and the normal vector of the lining surface is calculated, then the normal component is obtained by multiplying the normal vector by the dot product value, and finally the tangent component vector is obtained by subtracting the normal component from the gravity vector. The tangent component vector is the composition vector direction of the water film gravity flow.

[0088] When calculating the angle between the normal direction perpendicular to the lining surface and the opposite direction of the composition vector direction of the water film gravity flow, the following operations are performed: obtaining the normal direction vector of the lining surface, which is measured by a three-dimensional laser scanner at the detection point, such as the measured vector components. The dot product value of the normal direction vector and the composition vector of the water film gravity flow is calculated. The product value of the module length of the normal direction vector and the module length of the composition vector of the water film gravity flow is calculated. The cosine function value is obtained by dividing the dot product value by the module length product value. The angle value is calculated by calling the inverse cosine function. The angle value is the electromagnetic wave emission angle bias value, and the measurement unit is degree. Finally, the opposite number of the angle value is taken as the final bias value, for example, when the calculated angle value is 15 degrees, the electromagnetic wave emission angle bias value is negative 15 degrees.

[0089] When the electromagnetic wave emitter is driven to the direction of the normal direction plus the electromagnetic wave emission angle offset value, the closed loop control process is executed: the current angle sensor value of the electromagnetic wave emitter is read, for example, the absolute value encoder outputs the current azimuth angle. The target direction is calculated: the normal direction angle value plus the electromagnetic wave emission angle offset value, for example, the normal direction is 30 degrees, and the offset value is negative 15 degrees, then the target direction is 15 degrees. The target direction and the current direction are input into the proportional-integral-derivative controller, and the controller outputs the pulse width modulation signal. The pulse width modulation signal drives the servo motor to rotate, and the servo motor is connected to the electromagnetic wave emitter turntable through a reduction gearbox. When the angle sensor detects that the difference between the current direction and the target direction is less than 0.1 degrees, the controller stops outputting the signal. After the adjustment is completed, the turntable position is fixed by a mechanical locking device.

[0090] When the amplitude of the original electromagnetic wave signal is multiplied by the electromagnetic wave penetration energy compensation coefficient for energy compensation, an analog multiplication circuit is used to realize signal amplitude scaling. The original electromagnetic wave signal is output by the receiving antenna, and after being amplified by the preamplifier, it is input into the first input end of the multiplier in the form of a voltage waveform. The electromagnetic wave penetration energy compensation coefficient is input into the second input end of the multiplier in the form of a direct current voltage, and the voltage value comes from the output circuit of step S3. The multiplier chip selects AD734, and the output calculation formula is that the output voltage is equal to the first input voltage multiplied by the second input voltage and then divided by the reference voltage. The reference voltage is fixed at, for example, 10 volts. When the original signal amplitude is, for example, 2 volts peak-to-peak, and the compensation coefficient voltage is 0.7 volts, the output compensated signal amplitude is calculated as 2x0.7 / 10=0.14 volts peak-to-peak. The compensated signal is sent into the filter circuit after being buffered by the voltage follower. The linearity of the multiplier is calibrated, and within the input compensation coefficient range of 0.5 to 1.5 volts, the output error is less than ±1%.

[0091] When the center frequency of the band-pass filter is set based on the electromagnetic wave emission angle offset value, a pre-stored calibration mapping table is called. The mapping table is obtained by antenna pattern test: the transmitting antenna is fixed in the microwave darkroom, a receiving probe is set at a distance of, for example, 3 meters from the antenna, and the probe is connected to a three-dimensional mechanical turntable. The turntable is controlled to rotate at a step of 0.5 degrees, and the signal strength corresponding to each angle is measured within the range of -30 degrees to +30 degrees in the horizontal plane. For each test angle, the frequency corresponding to the maximum signal strength is determined as the center frequency by sweeping the frequency from 50 megahertz to 1 gigahertz. Finally, a corresponding relationship table of the electromagnetic wave emission angle offset value and the center frequency is established, for example, when the offset value is -15 degrees, the corresponding center frequency is 320 megahertz. In real-time processing, according to the electromagnetic wave emission angle offset value output by step S4 (for example, -15 degrees), the mapping table is queried to obtain the center frequency value (320 megahertz), and the value is written into the frequency control register of the programmable band-pass filter.

[0092] When the energy-compensated signal is spatially directionally filtered, a fourth-order Butterworth active filter circuit is used. The center frequency of the filter is set by a digital potentiometer, and the resistance value of the digital potentiometer is calculated by the microcontroller according to the center frequency value.

[0093] For example, when the center frequency is 320 MHz, the resistance value is calculated as

[0094] ;

[0095] wherein a standard capacitance C = 10 pF is taken, and R ≈ 49.8 Ω. The resistance value of the digital potentiometer AD5292 is set to 50 Ω (the closest value). The quality factor of the filter is fixed at, for example, 5, and the bandwidth is calculated as 64 MHz (320 / 5). The energy-compensated signal is input to the input end of the filter, and the spatially directionally filtered signal is obtained at the output end. The -3 decibel bandwidth of the filter output signal covers the frequency band of 256 MHz to 384 MHz, and suppresses the interference signals in the non-main lobe direction.

[0096] When detecting the lining-surrounding rock interface reflection peak point in the time-domain waveform of the filtered signal, the following digital signal processing procedure is used: first, the filtered signal is analog-to-digital converted at a sampling rate of 1 GHz and stored as a discrete time sequence. The time sequence is subjected to a moving average filtering, and the window width is set to, for example, 5 ns (corresponding to 5 sampling points). The first-order differential sequence of the waveform is calculated, and the candidate peak point is located by zero-crossing detection. A dynamic detection threshold is set: the root mean square value of the noise segment of the time-domain waveform in the first 50 ns is multiplied by a coefficient, for example, the coefficient is taken as 5.0, as the threshold reference. When the amplitude of the candidate peak point exceeds the threshold reference and is a local maximum value, it is determined as an effective reflection peak point. The index position of the point in the time sequence is recorded, and multiplied by the sampling interval of 1 ns to obtain the absolute time value. The time value is the time corresponding to the lining-surrounding rock interface reflection peak point, which is output as the effective echo time.

[0097] ​The correspondence between the center frequency of the band-pass filter and the angle offset value of the electromagnetic wave emission is calibrated by executing a standardized measurement procedure during the antenna pattern test: the transmitting antenna is installed at the center of the turntable in the microwave anechoic chamber, and the receiving antenna is fixed on the positioning frame 3 meters away from the transmitting antenna. The turntable controller rotates the transmitting antenna at a step of 0.5 degrees, and at each angle position, the following operations are performed: control the vector network analyzer to output a sweep signal (50-1000 MHz, step 1 MHz), and record the power value at the receiving end. After completing the full-angle scan, the following operations are performed on each angle data: find the frequency corresponding to the maximum power value, and record it as the center frequency corresponding to the current angle. Finally, the angle-frequency mapping table is generated and stored in the electrically erasable programmable read-only memory. The calibration process is repeated three times to take the average value, for example, the center frequencies measured at the -15 degree position are 318 MHz, 321 MHz, and 320 MHz, and the average value is 320 MHz.

[0098] When obtaining the effective echo time of the lining-surrounding rock interface, the time-domain waveform data stored in the digital signal processor is called. The effective echo time is from the peak detection output of step S5, and the unit of measurement is nanoseconds, for example, the recorded value is 65.3 nanoseconds. At the same time, the pre-stored reference propagation speed of electromagnetic waves in concrete is read from the non-volatile memory. The reference propagation speed is obtained through laboratory calibration, and the specific method is as follows: prepare a standard concrete test block (with the same mix proportion as the actual lining), and measure the propagation time delay of electromagnetic waves in the test block by transmission method; measure the geometric thickness of the test block; calculate the propagation speed equal to twice the thickness divided by the time delay (because electromagnetic waves propagate back and forth). For example, the thickness of the test block is 300 mm, and the measured time delay is 3.33 nanoseconds, so the reference propagation speed is calculated as (2×0.3) / (3.33×10 -9 )≈1.8×10 8 m / s. The value is stored as a floating-point number.

[0099] The operation of multiplying the effective echo time by the reference propagation speed to obtain the original thickness value is performed by the arithmetic logic unit. The effective echo time is converted to seconds: for example, 65.3 nanoseconds is equal to 6.53×10 -8 seconds. The reference propagation speed remains 1.80×10 8 m / s. The multiplication formula is: original thickness value=effective echo time×reference propagation speed÷2 (because the echo time is the round-trip time). The specific calculation process is as follows: first, store the effective echo time in register R1 and the reference propagation speed in register R2; calculate R3=R1×R2; then calculate R4=R3 / 2; finally, convert the unit to millimeters: R5=R4×1000 mm. The original thickness value is temporarily stored in the random access memory.

[0100] When calibrating the original thickness value based on the fixed distance from the transmitting end to the lining surface, the fixed distance is first measured. The fixed distance refers to the vertical distance from the center point of the antenna radiation surface to the lining surface, which is measured in real time using a laser range finder: a laser transmitter is installed on the side of the antenna support and projects laser light at a 45-degree angle to the lining surface; a receiver captures the reflected light spot and calculates the distance based on the time of flight. For example, the measured distance value is 50.2 mm. The time delay offset corresponding to the fixed distance is calculated as: time delay offset = 2 x fixed distance ÷ light speed. The light speed is 2.998 x 10 8 meters per second, for example, the fixed distance of 50.2 mm is converted to 0.0502 meters, and the time delay offset = 2 x 0.0502 ÷ 2.998e8 ≈ 0.335 nanoseconds. The calibration operation performs subtraction: the effective echo time minus the time delay offset, for example, 65.3 nanoseconds - 0.335 nanoseconds = 64.965 nanoseconds. The thickness is recalculated as 584.685 mm using the calibrated echo time.

[0101] When the calibrated original thickness value is output as the actual thickness of the lining, data formatting processing is performed: the thickness value calculated by calibration is read, for example, 584.685 mm; the last digit after the decimal point is taken (rounded) to get 584.7 mm; the position number and timestamp of the detection point are appended; and the data is output to the display device through a serial communication interface. The thickness value has a dimension of millimeters, and the effective range is limited to between 100 mm and 2000 mm, and an abnormal data alarm is triggered when the range is exceeded.

[0102] The complete detection scheme constituted by steps S1 to S6 of the embodiment forms a multi-dimensional collaborative perception mechanism for water-containing lining structures through the coupling correlation (steps S1-S2) of the dual-frequency reflected wave intensity difference and the gradient change rate of the water film dielectric constant, the dynamic energy compensation based on the gradient change rate (step S3), the vector collaborative adjustment of the gravity flow direction and the transmission angle (step S4), and the time-space joint filtering of the compensated signal (step S5). It breaks through the limitation of traditional methods that only regard the water film as a disturbance factor, and uses the gradient change of the water film dielectric property as a physical medium to transform the adverse condition of attenuating electromagnetic wave energy into a favorable information carrier for characterizing the structure state. The dynamic generation of the compensation coefficient based on the gradient change rate in step S3 is combined with the real-time adjustment of the transmission angle according to the gravity flow direction in step S4, which collaboratively suppresses the signal dispersion effect caused by the water film flow, so that the signal-to-noise ratio of the lining-rock interface echo extracted in step S5 is improved.

[0103] Embodiment 2: Figure 2 A structural diagram of a tunnel lining thickness real-time detection system is given, and the tunnel lining thickness real-time detection system comprises the following modules:

[0104] The dual-frequency reflection module is used for synchronously emitting electromagnetic waves of a first frequency and electromagnetic waves of a second frequency to the lining surface, and obtaining a dual-frequency reflection wave intensity difference of a concrete-water film interface.

[0105] The dielectric gradient module is used for calculating a water film dielectric constant gradient change rate according to the dual-frequency reflection wave intensity difference.

[0106] The compensation calculation module is used for determining an electromagnetic wave penetration energy compensation coefficient based on the water film dielectric constant gradient change rate.

[0107] The angle biasing module is used for calculating an electromagnetic wave emission angle biasing value according to a tunnel axis line inclination angle and a water film gravity flow direction, and adjusting an electromagnetic wave emission device orientation.

[0108] The echo extraction module is used for correcting original electromagnetic wave signals collected by a receiving end by using the electromagnetic wave penetration energy compensation coefficient and the electromagnetic wave emission angle biasing value, and extracting an effective echo time of a lining-surrounding rock interface.

[0109] The thickness calculation module is used for calculating an actual lining thickness according to the effective echo time and a reference propagation speed of electromagnetic waves in concrete.

[0110] The calculations involved in the embodiments are all de-dimensioned to obtain numerical calculations, and preset parameters and threshold values in the calculations are set by a person skilled in the art according to actual conditions.

[0111] The above embodiments can be realized wholly or partially by software, hardware, firmware or any other combination. When realized by software, the above embodiments can be realized in the form of a computer program product wholly or partially.

[0112] Those skilled in the art can realize that the modules and algorithm steps of the examples described in combination with the embodiments disclosed herein can be realized by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are realized in hardware or software depends on the specific application and the constraints of the technical solution. A person skilled in the art can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0113] In addition, each functional module in each embodiment of the present application can be integrated in one processing module, or each module can exist physically independently, or two or more modules can be integrated in one module.

[0114] In several embodiments provided in the present application, it should be understood that the disclosed system, device and method can be implemented in other manners. For example, the division of the above-described device embodiment is only a logical function division, and there can be another division manner for actual implementation, for example, multiple devices or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections between different parts can be indirect couplings or communication connections through some interfaces, devices or modules, and can be in electrical, mechanical or other forms.

[0115] The above describes only the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any modification or replacement within the technical range disclosed by the present application can be easily thought by any person skilled in the art, and should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0116] Finally: the above described is only the preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for real-time detection of tunnel lining thickness, characterized in that, Includes the following steps: S1. Simultaneously transmit first frequency electromagnetic waves and second frequency electromagnetic waves to the lining surface to obtain the intensity difference of the dual-frequency reflected waves at the concrete-water film interface. S2. Calculate the gradient rate of change of the dielectric constant of the water film based on the intensity difference of the dual-frequency reflected waves, including: Based on the fixed difference between the reference value of the dielectric constant of concrete and the relative dielectric constant of water, a linear mapping relationship between the intensity difference of dual-frequency reflected waves and the change of dielectric constant is established. The intensity difference of the dual-frequency reflected waves is input into a linear mapping relationship, and the change in the dielectric constant of the water film is output. Divide the change in the dielectric constant of the water film by the frequency difference between the first frequency electromagnetic wave and the second frequency electromagnetic wave to obtain the gradient rate of change of the dielectric constant of the water film. S3. Determine the electromagnetic wave penetration energy compensation coefficient based on the gradient rate of change of the dielectric constant of the water film, including: Establish a positive proportional relationship between the gradient rate of change of the dielectric constant of the water film and the attenuation rate of electromagnetic wave energy; The basic compensation coefficient is obtained by multiplying the rate of change of the dielectric constant gradient of the water film by the proportionality constant. A fixed constant is superimposed on the basic compensation coefficient to form the electromagnetic wave penetration energy compensation coefficient; S4. Calculate the electromagnetic wave emission angle offset value based on the tunnel axis inclination and the direction of water film gravity flow, and adjust the orientation of the electromagnetic wave emission device, including: Read the tunnel axis inclination angle in the design drawings and fix the gravity flow direction of the water film as vertically downward; A vector synthesis relationship between the tunnel axis inclination angle and the direction of water film gravity flow is established based on Newton's laws of motion; The angle between the direction of the normal perpendicular to the lining surface and the opposite direction of the resultant vector of the water film gravity flow is calculated as the electromagnetic wave emission angle offset value. The servo motor is driven to orient the electromagnetic wave emitting device toward a direction that is adjusted to the normal direction and superimposed with the electromagnetic wave emission angle offset value. S5. The electromagnetic wave signal collected by the receiver is corrected by the electromagnetic wave penetration energy compensation coefficient and the electromagnetic wave emission angle offset value, and the effective echo time of the lining-surrounding rock interface is extracted. S6. Calculate the actual thickness of the lining based on the effective echo time and the reference propagation speed of electromagnetic waves in concrete.

2. The method for real-time detection of tunnel lining thickness according to claim 1, characterized in that, Simultaneously emitting first-frequency electromagnetic waves and second-frequency electromagnetic waves onto the lining surface, and obtaining the intensity difference of the dual-frequency reflected waves at the concrete-water film interface, including: Simultaneously emit electromagnetic waves of the first frequency and the second frequency in a direction perpendicular to the lining surface; The intensity values ​​of the first frequency reflected wave and the second frequency reflected wave are collected at the same receiving point on the concrete-water film interface by the receiving end. The algebraic difference between the intensity values ​​of the first frequency reflected wave and the intensity values ​​of the second frequency reflected wave is taken as the intensity difference of the dual-frequency reflected wave.

3. The method for real-time detection of tunnel lining thickness according to claim 2, characterized in that, The first frequency electromagnetic wave has a frequency range of 100MHz to 200MHz, and the second frequency electromagnetic wave has a frequency range of 500MHz to 600MHz.

4. The method for real-time detection of tunnel lining thickness according to claim 1, characterized in that, The proportionality constant was determined through comparative tests of dry concrete specimens and water-containing concrete specimens.

5. The method for real-time detection of tunnel lining thickness according to claim 1, characterized in that, The original electromagnetic wave signal acquired by the receiver is corrected using an electromagnetic wave penetration energy compensation coefficient and an electromagnetic wave emission angle offset value. The effective echo time of the lining-surrounding rock interface is then extracted, including: Energy compensation is performed by multiplying the amplitude of the original electromagnetic wave signal by the electromagnetic wave penetration energy compensation coefficient. The center frequency of the bandpass filter is set based on the electromagnetic wave emission angle offset value, and the energy-compensated signal is then subjected to spatial directional filtering. The peak reflection point at the lining-surrounding rock interface is detected in the time-domain waveform of the filtered signal, and the time corresponding to the peak reflection point at the lining-surrounding rock interface is recorded as the effective echo time. The relationship between the center frequency of the bandpass filter and the electromagnetic wave emission angle offset value is calibrated through antenna pattern testing.

6. The method for real-time detection of tunnel lining thickness according to claim 1, characterized in that, The actual thickness of the lining is calculated based on the effective echo time and the reference propagation speed of electromagnetic waves in concrete, including: Obtain the effective echo time at the lining-surrounding rock interface and call the pre-stored reference propagation speed of electromagnetic waves in concrete. Multiply the effective echo time by the reference propagation speed to obtain the original thickness value; The time-domain waveform start offset is calibrated based on the fixed distance from the transmitter to the lining surface to calibrate the original thickness value. The calibrated original thickness value is used as the actual thickness of the lining.

7. A real-time tunnel lining thickness detection system, used to implement the real-time tunnel lining thickness detection method according to any one of claims 1-6, characterized in that, Includes the following modules: The dual-frequency reflection module is used to simultaneously transmit first-frequency electromagnetic waves and second-frequency electromagnetic waves to the lining surface to obtain the intensity difference of the dual-frequency reflected waves at the concrete-water film interface. The dielectric gradient module is used to calculate the gradient rate of change of the dielectric constant of the water film based on the intensity difference of the dual-frequency reflected waves. The compensation calculation module is used to determine the electromagnetic wave penetration energy compensation coefficient based on the gradient change rate of the dielectric constant of the water film. Angle offset module is used to calculate the electromagnetic wave emission angle offset value based on the tunnel axis inclination and the gravity flow direction of the water film, and to adjust the orientation of the electromagnetic wave emission device. The echo extraction module is used to correct the original electromagnetic wave signal collected by the receiver by using the electromagnetic wave penetration energy compensation coefficient and the electromagnetic wave emission angle offset value, and to extract the effective echo time of the lining-surrounding rock interface. The thickness calculation module is used to calculate the actual thickness of the lining based on the effective echo time and the reference propagation speed of electromagnetic waves in concrete.

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